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Mirena: The hormonal IUD

Dear Alice,

It looks to me like that the contraceptive patch and the NuvaRing work in a similar way, but I don't understand how the Mirena (or any IUD, really) works. Why might these methods be better than oral contraceptives that have been out for a long time?

— Thinking about trying a new method

Dear Thinking about trying a new method,

Good question! It is important to be in the know about a variety of birth control options, since new ones are being developed and may be a better "fit" for you than what you are currently using.

The contraceptive patch and the contraceptive ring (NuvaRing) do work similarly. The contraceptive patch is essentially a sticker that is applied weekly to the surface of the skin that uses norelgestromin (a progestin) and ethinyl estradiol (an estrogen) to significantly decrease the chances of pregnancy. The contraceptive ring is a small polymer ring that is inserted into the vagina for three weeks. It uses the same hormones as the patch to prevent pregnancy. The ring must be removed for one week, when a woman menstruates — during that time, a woman is still protected from becoming pregnant. After her period has finished, a new ring can be inserted. For more specific information on these two methods, check out the Related Q&As.

Mirena is a commercially-available, U.S. Food and Drug Administration (FDA) -approved intrauterine device (IUD). IUDs are contraceptive devices, either coiled or T-shaped, inserted by a health care provider that sit in a woman's uterus, just past the cervix. Depending on which type a woman uses, IUDs can prevent pregnancy from one to ten years, and can be removed at any time by a health care provider, if pregnancy is desired. IUDs have proven to be as effective or even more effective than birth control pills (especially among women who have had a child or children), though specialists are still not certain as to precisely how they work. Mirena is a hormone-releasing IUD. This presents various benefits, including:

High efficacy: In a clinical trial, fewer than one in 100 women using Mirena became pregnant during five years of use. Mirena can be used for up to five years, and a new device can be inserted after five years if a longer period of protection is desired.

Hormonal regulation: Mirena releases a hormone called levonorgestrel into the uterus. Levonorgesterel is a progestin hormone used in several progestin-only birth control pills, as well as in the Plan B emergency contraception method.

Lighter periods: Using Mirena can reduce excessive menstrual bleeding. In fact, women who use Mirena have reported that their bleeding diminished from seven to two days during the first year of usage. Mirena has also been shown to reduce blood loss caused by uterine fibroids

Convenience: a single insertion can be effective for up to five years without the necessity of strictly adhering to a daily, weekly, or monthly contraceptive method. This means not having to remember to frequently take a pill or replace a patch or a ring. Some women find that this enhances their sexual experiences.

Low cost: although the initial medical exam, insertion, and follow-up appointments may be expensive, using an IUD may save you big bucks compared to the monthly cost of the pill, the patch, or the ring.

In the end, deciding between Mirena, the pill, the contraceptive ring, the contraceptive patch, or any other method is a choice you can make with your women's health care provider or gynecologist and/or partner. Your provider can discuss with you the many options available for contraception and, dependent on your medical history, lifestyle, sexual activity, and any medication you might be taking, can recommend specific choices that would best suit you. Lastly, none of the methods of contraception mentioned above prevent against sexually transmitted infections (STIs). For this kind of protection, latex condoms (and other barrier methods) are still the best option.